1. Field of the Invention
The present invention relates to a spectrum spread communication and in particular to a (multi-rated) multiplexing direct spread spectrum communication having a variable multiplicity in which the transmission power is made constant.
2. Description of the Relates Art
Recently spread spectrum communication systems have attracted attention as new communication systems. The modulation schemes used for general data transmission are narrow band modulation scheme. Although they can be implemented by a relatively small circuit, they have a disadvantage that they are susceptible to multipath phasing and colored noise in a narrow band indoors (offices, factories).
In contrast to this, the spread spectrum communication systems are advantageous in that the above-mentioned disadvantage is overcome since the spectrum of data is spread with a spreading code for transmission in a broad band.
However, high rate data transmission is hard to conduct since the wider band is required for the higher data transmission rate. For example, if data transmission using QPSK (Quadrature Phase Shift Keying) scheme by spreading data with a 11 chips is contemplated, 22 MHz band is required for 2 Mbps data transmission. 110 MHz band is required for data transmission at a rate of 10 Mbps.
Further, regulation of bands in which radio wave transmission is permitted also makes it harder to conduct high rate data transmission.
Accordingly, in order to conduct high rate transmission in a restricted band, a multiplexing scheme in which spread signals are delayed (hereinafter referred to as xe2x80x9cdelay multiplexing scheme) is proposed (refer to Japanese Laid-Open Patent Publication No. 9-55714).
Use of this scheme makes it possible to conduct high rate transmission in a restricted band. If the scheme which is disclosed in the cited publication No. 9-55714 is used for the former example (2 Mbps data, 22 MHz band), duplexing and quintuplexing in the same band enables data transmission at 4 and 10 Mbps, respectively.
FIG. 1 is a block diagram showing an exemplary circuit used for heretofore proposed delay multiplexing scheme.
In FIG. 1, data which is generated by a data generating portion 110 is differentially coded by a differential encoding portion 111 and then parallel-converted into numbers to be multiplexed by an S/P converting portion 112.
Subsequently, the parallel data is spread by being multiplied by a PN code from a PN generator 114 by respective multiplying portions (113-1 through 113-4) and then delayed by respective delay elements (115-1 through 115-4).
Then, the delayed data are combined into multivalued digital signals by a combiner (frequency combining device) 116. The digital signals are modulated by an oscillated signal from an oscillator 120 in a modulator 119. The signal is transmitted via a frequency converting portion 122 and power amplifier 123.
As a result, high rate data transmission in a limited band is made possible.
In a telecommunications system using such a spectrum spreading, the transmission signal assumes +1 or xe2x88x921, and the multiplexed signal assumes multivalue in the multiplex part. For example, the quintuplexed signal assumes values of xe2x88x925, xe2x88x923, xe2x88x921, 1, 3, 5.
This is shown in FIG. 2. As shown in FIG. 2, the multiplexed operation values differ largely in simplex and multiplex parts.
On the other hand, in the communication system, the signal, the frequency of which is converted to a radio frequency range is usually transmitted. In this case, the operation value assumes 1 and xe2x88x921 in the simplex part and xe2x88x925, xe2x88x923, xe2x88x921, 1, 3, 5 in the quintuplex part, so that the transmission outputs are not identical in the simplex and multiplex parts.
For the spread spectrum communications in Japan, the communication system using ISM (Industrial, Scientific and Medical) band is permitted as special low power communication system in an assigned band in Japan. A standard RCR-STD-33 (RCR: Research and Development Center for Radio System) is established.
In this standard, usable bands, physical specifications such as allowed power are determined. As to transmission power, it is regulated that the filed transmission power should be kept except for several tolerances.
Accordingly, there is the risk of transmission of the power exceeding the standards if the signal as multiplexed is amplified with the same amplification and is output.
It is also preferable for a high power amplifier in a transmitter system and for an amplifier in a receiver that the power is equal in the simplex/multiplex parts. Use of the system which can not satisfy these requirements provides problems.
The other circuit systems in the communication system in interest are shown in FIGS. 3 and 4.
The differences between the circuits of FIGS. 1 and 3 reside in the difference in the multiplication and in that detection and control portion 121c and gain-variable amplifier 121 are additionally provided in the latter circuit.
FIG. 4 shows a variation of the configuration of FIG. 3 for conducting the spreading, delaying and adding operations in a digital manner and is substantially identical with the configuration of FIG. 3 except that the signal is delay-multiplexed by means of multipliers 113xe2x80x2-1 through 113xe2x80x2-5, delay elements 115xe2x80x2-1 through 115xe2x80x2-5 and operating portions 117, and is thereafter D/A converted by a D/A convertor 118 and is input to a modulator 119.
As shown in FIGS. 3 and 4, some communication systems have a gain-variable amplifier 121, the gain of which is changed in response to a signal from the detection and control portion 121c which detects the power of the transmission system for controlling the transmission output to a constant output.
The gain-variable amplifier 121 is disposed at the succeeding stage of the modulator 119 for reducing or eliminating variations of elements in the system such as lowering of output which may be caused by variations in characteristics such as temperature characteristics among the elements and aging of elements.
The detection and control portion 121c usually determines the power of RF or IF signal after the modulator 119 as a signal to be controlled for controlling the gain-variable amplifier 121 to keep the power of the signal after detection in response to determined power.
Since the control operation inherently contemplates to absorb the variations among systems, the time constant of integration is set comparatively longer so that the characteristics will not be varied due to noise. The characteristics when a signal having the simplex/multiplex part is input to this circuit is shown in FIG. 5.
FIG. 5(A) shows the changes in the output power on the input side of the gain-variable amplifier 121. FIG. 5(C) shows the output when the gain is variably changed. FIG. 5(B) shows the control voltage when the above-mentioned time constant of integration is set comparatively longer.
As shown in FIG. 5(C), there is a problem that in the transient period, the transmission power will largely increase by the amount corresponding to the integration interval at the transient although the transmission power is kept constant after the lapse of the considerable period of time.
It is an object of the present invention to provide a direct spread spectrum communication system using a multi-rated delay multiplexing scheme, the multiplicity of which is changed, the system performing control operation as quickly as possible by suppressing the output fluctuation within a narrow range so as to perform constant power transmission.
In accordance with the present invention, there is provided a transmitter for a multi-rated delay multiplexing direct spread spectrum communication system including delay multiplexing means for multiplexing a plurality of series of signals which are obtained by delaying, by a desired number of chips, each of the signals. The signals are directly spread with the same spreading code. Transmission processing means is included for generating transmission signals by modulating the signals which have been multiplexed by the delay multiplexing means and by changing the frequency band of them, in which multi-rated transmission signals are generated in a format having a simplex part and a multiplex part having a given multiplicity. There is also provided control means for controlling the transmission power so that it is constant, and in which the control means performs a control operation depending upon the multiplicity of the format.
In accordance with the present invention, said control means changes its control operation in response to a multiplicity representing signal which is determined by said format when the multiplexing operation is switched in response to the multiplicity representing signal for making the transmission power constant for each multiplicity.
In accordance with the present invention, the transmitter comprises: detecting means for detecting the output transmission power in said transmission processing means; and means for controlling the amplified output of said transmission processing means in response to the detection output of said detecting means; and in that the time constant of the integration of said detecting means is reduced in response to a multiplexing switching signal which is defined by said format at the transient at which multiplexing is switched.
In accordance with the present invention, the transmitter comprises: detecting means for detecting the output transmission power in said transmission processing means; and means for controlling the amplified output of said transmission processing means in response to the detection output of said detecting means; and the time constant of the integration of said detecting means is reduced in response to a signal representing a simplex part in said format and a multiplexing switching signal which is defined by said format at the transient at which multiplexing is switched.
In accordance with the present invention, the transmitter comprises: detecting means for detecting the output transmission power in said transmission processing means; control means for controlling the amplified output of said transmission processing means in response to the detection output of said detecting means; and means for converting the amplitude of the control signal from said controlling means in response to a multiplexing signal which is defined by the format.
In accordance with the present invention, if a digital operation is performed in the delay multiplexing means as one of the control means, changing of a multiplier for the data to be multiplexed in the digital operation depends upon a signal representative of the multiplicity. The signal is determined by the format, so that the average amplitude is constant in a square root among multiplicity including simplex.
In accordance with the present invention, if a digital operation is performed in said delay multiplexing means, a numerical value table which is referenced by the multiplexing data of the result of said digital operation is used as one of said control means; and data is output which makes the transmission power constant by changing said numerical value table in response to a signal representative of the multiplicity which is determined by said format.
In accordance with the present invention, for each multiplicity, there are the numerical value tables having numerical values which make the converted transmission power constant even if the numerical values which are given to a D/A convertor for D/A data conversion after referencing to one of the numerical value tables are discrete values, and the numerical value table is selected depending upon a signal representative of the multiplicity which is determined by the format.
In accordance with the present invention, if the Barker code of 11 chips is multiplexed and a 8 bit D/A convertor is used, the numerical value which is provided in each of said numerical value tables is
xe2x88x9238, 38 when simplexing
xe2x88x9254, 0, 54 when duplexing
xe2x88x9266, xe2x88x9222, 22, 66 when triplexing
xe2x88x9276, xe2x88x9238, 0, 38, 76 when quadruplexing
xe2x88x9285, xe2x88x9251, xe2x88x9217, 17, 51, 85 for quintuplexing.
In accordance with the present invention, there is provided a receiver for multi-rated delay multiplexing direct spread spectrum communication system having receiving and processing means for receiving signals. The signals are transmitted at a equal transmission output irrespective of the multiplicity, by multi-rating the signals which are a spreading-code-spreaded, in a format having a multiplex part. A plurality of series of signals are each delayed by a desired number of chips and a simplex part. Also, the gain adjustment in the receiving and processing means, on reception, is conducted depending upon a correlation output value. A reference comparison value is compared with the correlation output value for generating a control signal of the gain adjustment which is preset to a comparison value depending upon a power ratio of the multiplicity by a multiplexing switching portion based upon the format.
In accordance with the present invention, there is provided a receiver for multi-rated delay multiplexing direct spread spectrum communication system having receiving and processing means for receiving signals. The signals are transmitted at a equal transmission output irrespective of the multiplicity, by multi-rating the signals which are a spreading-code-spreaded, in a format having a multiplex part. A plurality of series of signals are each delayed by a desired number of chips. The gain adjustment in the receiving and processing means on reception is conducted depending upon a correlation output value. The correlation output value is compared with a reference comparison value and used for generating a control signal for gain adjustment. A correlation output value, which is obtained by converting a correlation signal received from a multiplexing switching portion based upon the format, depends upon the power ratio of its multiplicity.
In accordance with the present invention, there is provided a multi-rated delay multiplexing direct spread spectrum communication system comprising: the inventive transmitter; and the inventive receiver.